This invention relates generally to improved serial digital transmission means and methods, and more particularly to improved means and methods useful for providing reliable, high speed communication of digital data between units in a digital data processing system.
Modern data processing systems have a number of different units between which binary digital data must be communicated economically at high speed and over long distances. The problems associated with a system to satisfy the above requirements are to transmit data over one transmission medium with only one transition per bit and with a clock imbedded in the data. In addition, it is often a requirement to provide means for non-continuous operation so that data transmission may be started and stopped. In addition to direct coupling, it is advantageous to have the capability to transmit the data with no long term DC component in the transmitted waveform so that transformer isolation may be used at the ends of the transmission line to electrically isolate separated units which are likely to have different ground potentials.
Although a variety of approaches and circuitry are known in the art for implementing a serial digital data transmission system, most prior art will solve certain ones but not all of the aforementioned problems. Methods which are theoretically capable of solving all of the above problems involve complicated coding schemes and require considerable logic circuitry for implementation of coding and decoding, or require burst methods with start and stop bits which reduces the overall bit transfer rate.